The present invention relates to a traffic crash attenuation system or crash cushion system. More particularly, the present invention relates to a system, method and apparatus for absorbing kinetic energy from an impacting vehicle in a controlled and safe manner. The system is used with roadside safety devices such as guardrails and median barrier end treatments. Even more specifically, the present invention is a system applied to shield bridge piers in the median of divided highways.
Current safety treatments at bridge pier sites include installation of guard rails on each side of the piers to form an envelope with W-beam bullnose ends. In some applications, crash cushions are installed on the two ends of the pier configuration with concrete walls constructed in the spaces between adjacent piers.
The present system consists of two energy-absorbing crash cushions combined with a tubular frame or structure to envelop the bridge piers. The crash cushions provide protection for end-on impacts while the tubular side structure shields the bridge piers from oblique impacts by errant vehicles. The tubular structure around the bridge piers is modular in nature and can be adjusted to accommodate different number, size, and spacing of bridge piers. The energy-absorbing capabilities of this new crash cushion are based on tube bursting technology described in U.S. Pat. Nos. 6,308,809 and 6,437,570 and incorporated herein by reference. This basic “guardrail envelope” treatment has some limitations which the present invention addresses.
Initial testing of prototypes of the present invention indicated snagging of the engine hood and the left-front fender on the upstream side of the bridge pier, thus causing the engine hood to be pushed backward and into the base of the windshield. This engine hood to windshield contact resulted in noticeable damage to the windshield. Based on the engine hood snag and resulting windshield damage, there was a potential for penetration of the occupant compartment during impact. The present invention avoids the hazards posed by interaction of vehicles with the bridge piers. This has been evidenced by crash testing utilizing a pickup truck weighing approximately 2,000 Kg impacting the present invention system at a speed of 100 km/h and at an angle of 25 degrees at the critical impact point (CIP) of the system.
Testing revealed that there must be sufficient space between the guardrail side structure and the adjacent face of any of the bridge piers to allow for the dynamic deflection of the guardrail. Without this space, an impacting vehicle may reach and impact the pier. An excessive space between the guardrail side structure and the pier, such as may occur when the guardrail is installed on a sloping grade away from the pier, may adversely effect the performance of the guardrail.
The present invention solves these problems of protecting vehicles from impacting bridge piers.